Laboratory experiments examining oscillatory flow along a coastline or isobath with a series of headlands or ridges reveal a mechanism for transfer of momentum and mass from the boundary into the interior flow through the establishment of organized residual flow patterns. Particle imaging velocimetry is used to visualize the vorticity field and to quantify large-scale residual circulations generated near the region of roughness. Two flow regimes are observed for differing ratios of along-coast tidal excursion, L, to the length of the roughness region, D. For L/D > 1 a weak inflow is produced in the vicinity of the roughness region, with a corresponding alongshore flow away from the region. For L/D < 1 a strong outflow jet is established near the center of the roughness region. The two flow regimes result from different residual vorticity patterns and rely on eddies being long-lived relative to the tidal period. Thus these results are relevant to flows in which dissipation is weak relative to the mean flow kinetic energy such as for tidal flow in deep water. Flow past a single roughness element is used as an analog to tidal flow past a headland and is represented by the high L/D limit.